Separation of 2-methyl-1-propanol from 1-butanol by azeotropic distillation

ABSTRACT

2-Methyl-1-propanol is difficult to separate from 1-butanol by conventional distillation or rectification because of the proximity of their boiling points. 2-Methyl-1-propanol can be easily separated from 1-butanol by azeotropic distillation. Effective agents are isobutyl acetate, methyl cyclohexane and 2-nitropropane.

FIELD OF THE INVENTION

This invention relates to a method for separating 2-methyl-1-propanol from 1-butanol using certain organic compounds as the agent in azeotropic distillation.

DESCRIPTION OF PRIOR ART

Azeotropic distillation is the method of separating close boiling compounds or azeotropes from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid, said liquid forming an azeotrope with one or both of the compounds to be separated. Its presence on each plate of the rectification column alters the relative volatility in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The azeotrope forming agent is introduced with the feed to a continuous column. The azeotrope forming agent and the more volatile component are taken off as overhead product and the less volatile component comes off as bottoms product. The usual methods of separating the azeotrope former from the more volatile component are cooling and phase separation or solvent extraction.

The usual method of evaluating the effectiveness of azeotropic distillation agents is the change in relative volatility of the compounds to be separated. Table 1 shows the degree of separation or purity obtainable by theoretical plates at several relative volatilities. Table 1 shows that a relative volatility of at least 1.2 is required to get an effective separation by rectification.

                  TABLE 1                                                          ______________________________________                                         Effect of Relative Volatility on Theoretical Stage Requirements.               Separation Purity,                                                                        Relative Volatility                                                 Both Products                                                                             1.02   1.1     1.2 1.3  1.4 1.5  2.0 3.0                            (Mole Fraction)                                                                           Theoretical Stages at Total Reflux                                  ______________________________________                                         0.999      697    144     75  52   40  33   19  12                             0.995      534    110     57  39   30  25   14  9                              0.990      463    95      49  34   26  22   12  7                              0.98       392    81      42  29   22  18   10  6                              0.95       296    61      31  21   16  14   8   4                              0.90       221    45      23  16   12  10   5   3                              ______________________________________                                    

2-Methyl-1-propanol and 1-butanol boil ten degrees apart and have a relative volatility of 1.2 and are difficult to separate by conventional rectification. Table 2 shows that to get 99% purity, 67 actual plates are required. With an agent giving a relative volatility of 2.0, only 20 actual plates are required.

                  TABLE 2                                                          ______________________________________                                         Theoretical and Actual Plates Require vs. Relative                             Volatility for 2-Methyl-1-propanol-1-Butanol Separation                        Relative Theoretical Plates Required                                                                     Actual Plates                                        Volatility                                                                              At Total Reflux, 99% Purity                                                                     Required, 75% Eff.                                   ______________________________________                                         1.2      49               66                                                   1.4      26               35                                                   1.65     18               24                                                   2.0      12               16                                                   ______________________________________                                    

OBJECTIVE OF THE INVENTION

The object of this invention is to provide a process or method of azeotropic distillation that will enhance the relative volatility of 2-methyl-1-propanol from 1-butanol in their separation in a rectification column. It is a further object of this invention to identify effective azeotropic distillation agents that are stable and can be recycled.

SUMMARY OF THE INVENTION

The objects of this invention are provided by a process for the separation of 2-methyl-1-propanol from 1-butanol which entails the use of certain organic compounds when employed as the agent in azeotropic distillation.

                  TABLE 3                                                          ______________________________________                                         Effective Azeotropic Distillation Agents For                                   Separating 2-Methyl-1-propanol From 1-Butanol                                                        Relative                                                 Compounds             Volatility                                               ______________________________________                                         None                  1.2                                                      Tetrahydrofuran       1.6                                                      Cyclohexane           1.5                                                      Isopropyl acetate     1.55                                                     Propyl acetate        1.5                                                      Ethyl formate         1.75                                                     Butyl formate         1.5                                                      Isobutyl acetate      2.0                                                      Ethyl acetate         1.6                                                      Ethyl propionate      1.6                                                      Dimethyl carbonate    1.45                                                     Ethyl butyrate        1.45                                                     Methyl butyrate       1.5                                                      Diethyl malonate      1.4                                                      Methyl pivalate       1.45                                                     2-Pentanone           1.5                                                      Acetone               1.6                                                      2-Butanone            1.6                                                      3-Methyl-2-butanone   1.5                                                      Toluene               1.7                                                      3-Pentanone           1.7                                                      1-Octene              1.55                                                     Cyclohexene           1.6                                                      2,2,4-Trimethylpentane                                                                               1.7                                                      Benzene               1.65                                                     2,2-Dimethylpentane   1.65                                                     2,3-Dimethylpentane   1.65                                                     Methyl cyclohexane    1.65                                                     Isopropyl ether       1.6                                                      Ethyl ether           1.7                                                      Benzonitrile          1.4                                                      2-Dimethylamino-2-methyl-1-propanol                                                                  1.45                                                     Nitromethane          1.55                                                     Nitroethane           1.7                                                      1-Nitropropane        1.55                                                     2-Nitropropane        1.8                                                      ______________________________________                                    

DETAILED DESCRIPTION OF THE INVENTION

I have discovered that certain organic compounds will effectively increase the relative volatility between 2-methyl-1-propanol and 1-butanol during rectification when employed as the agent in azeotropic distillation. Table 3 summarizes the the data obtained with these agents. The agents which are effective are tetrahydrofuran, cyclohexane, isopropyl acetate, propyl acetate, ethyl formate, butyl formate, isobutyl acetate, ethyl acetate, ethyl propionate, dimethyl carbonate, ethyl butyrate, methyl butyrate, diethyl malonate, methyl pivalate, 2-pentanone, acetone, 2-butanone, 3-methyl-2-butanone, toluene, 3-pentanone, 1-octene, cyclohexene, 2,2,4-trimethylpentane, benzene, 2,2-dimethylpentane, 2,3-dimethylpentane, methyl cyclohexane, isopropyl ether, ethyl ether, benzonitrile, 2-dimethylamino-2-methyl-1-propanol, nitromethane, nitroethane, 1-nitropropane and 2-nitropropane.

THE USEFULNESS OF THE INVENTION

The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1, 2 and 3. All of the successful agents show that 2-methyl-1-propanol can be separated from 1-butanol by means of azeotropic distillation and that the ease of separation is considerable.

WORKING EXAMPLE

Example 1: Fifty grams of 2-methyl-1-propanol-1-butanol mixture and fifty grams of isobutyl acetate as the azeotrope forming agent were charged to a vapor-liquid equilibrium still and refluxed for two hours. The vapor composition was 83.8% 2-methyl-1-propanol and 16.2% 1-butanol; the liquid composition was 72.3% 2-methyl-1-propanol and 27.7% 1-butanol. This is a relative volatility of 2.0. 

I claim:
 1. A method for recovering 2-methyl-1-propanol from a mixture consisting of 2-methyl-1-propanol and 1-butanol which consists essentially of distilling said mixture consisting of 2-methyl-1-propanol and 1-butanol in the presence of an azeotrope forming agents, recovering the 2-methyl-1-propanol and the azeotrope forming agent as overhead product and obtaining the 1-butanol as bottoms product, wherein said azeotrope forming agent consists of one material selected the group consisting of tetrahydrofuran, cyclohexane, isopropyl acetate, propyl acetate, ethyl formate, butyl formate, isobutyl acetate, ethyl acetate, ethyl propionate, dimethyl carbonate, ethyl butyrate, methyl butyrate, diethyl malonate, methyl pivalate, 2-pentanone, acetone, 2-butanone, 3-methyl-2-butanone, toluene, 3-pentanone, 1-octene, cyclohexene, 2,2,4-trimethylpentane, benzene, 2,2-dimethylpentane, 2,3-dimethylpentane, methyl cyclohexane, isopropyl ether, ethyl ether, benzonitrile, nitromethane, 2-dimethylamino-2-methyl-1-propanol, nitroethane, 1-nitropropane and 2-nitropropane. 